Irreversible brain damage to the fetus frequently results from prolonged ischemia/hypoxia during pregnancy. Oxidants produced during ischemia- reperfusion can cause significant tissue damage if they overwhelm the body's antioxidant defenses. Pro-oxidant systems, like xanthine oxidase, develop earlier than antioxidant enzyme systems in the developing fetus. The hypothesis of this proposal is that oxidants derived from xanthine oxidase and nitric oxide are responsible for cortical fetal brain damage following acute hypoxia. The hypothesis will be tested using specific inhibitors to xanthine oxidase and nitric oxide generating systems in a preterm gestation rabbit model of acute fetal hypoxia. It is proposed: 1) to determine the involvement of xanthine oxidase in excess oxidant production, depletion of antioxidant defense systems, and brain injury following fetal hypoxia-reoxygenation. It is postulated that xanthine oxidase released into the circulation causes multi-system injury, including brain injury. The imbalance between oxidant production and antioxidant systems and the relationship to tissue injury will be investigated following interference with xanthine oxidase activity and administration of antioxidants. 2) to determine the involvement of nitric oxide in excess oxidant production, depletion of antioxidant defense systems, and brain injury following fetal hypoxia-reoxygenation. The interaction of nitric oxide with oxidants, including those derived from xanthine oxidase, will be investigated in fetal rabbits in vivo and in fetal neuronal and astrocyte cultures. The regulation of gene expression of xanthine oxidase, nitric oxide synthase (the enzyme that produces nitric oxide) and superoxide dismutase (a key antioxidant enzyme), and correlation with their enzymatic activity will be determine following acute hypoxia. Completion of the proposed research will broaden the understanding of basic mechanisms of oxidant-mediated fetal brain injury, and identify useful biochemical markers and pharmacological ameliorations of brain injury in fetal hypoxia. The laboratories of the sponsors and consultants provide a fertile atmosphere in which to do the proposed studies. The experience and training in neurobiology and molecular biology that the candidate will gain on completion of this proposal will form a solid framework for a successful investigative career.